Tailgate lift mechanism

ABSTRACT

Tailgate lift mechanism, embodying parallelogram-type linkage, has a platform which is arranged to lift loads from ground level to the bed level of a truck body, and is also arranged to swing to vertical gate-closing position. There is power-operated means for controlling the movement from ground level to bed level, and separate power-operated means for raising the platform to gateclosing position. The last power-operated means includes linkage which is movable to an over-center closing position to provide a firm closure and to protect against accidental dropping of the gate.

United States Patent Glomski et a].

[111 3,883,014 [451 May 13, 1975 [54] TAILGATE LIFT MECHANISM 3,344,215; 12/1337 lgugle 49/340 3,589, l l t I4 77 PX [75] Inventors: Norman J. Glomski, New Berlm; ersen Jackman waukesha bot Primary ExammerRobert J. Spar Assistant Examiner-L. J. Paperner Assigneei The Heil Milwaukee, Attorney, Agent, or FirmArthur L. Morsell, Jr.

[22] Filed: Nov. 5, 1973 21 App]. No.: 413,087 [57] ABSTRACT Tailgate lift mechanism, embodying parallelogramtype linkage, has a platform which is arranged to lift 214/77 2g J loads from ground level to the bed level of a truck "I body, and is also arranged to Swing to vertical gated of Search Z closing position. There is power-operated means for controlling the movement from ground level to bed level, and separate power-operated means for raising [56] References cued the platform to gate-closing position. The last power- UNITED STATES PATENTS operated means includes linkage which is movable to 2,593,240 4/1952 Anthony et a1. 296/57 AX an over-center closing position to provide a firm clo- 2,725,152 11/1955 Gwinn sure and to protect against accidental dropping of the 2,739,484 3/1956 Orr gam 2,792,135 5/1957 Wood 2,850,187 9/1958 Roberts 214/77 P 7 Claims, 6 Drawing Figures N; 27 M \l -r igi 3 ,a '3.

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57 34 I! I 4 44 5'1 35 W I 52 5 42 26 5 ll 7 f ,25 46 4a 27 4/ 5 7 zz PATENTED RAY I 31975 SHEET 1 [if P -3m n um I 31915 SHEET 2 [IF POSITION 1 BEFORE CENTER POSITION 2 ON CENTER POSITION 3 OVER CENTER (AND LOCKED) TAILGATE LIFT MECHANISM BACKGROUND OF THE INVENTION l. Field of the Invention The present invention is adapted for use in connection with truck bodies to assist in moving loads to and from bed level and to serve as a tailgate closure.

2. Description of the Prior Art Tailgate lifts have heretofore been proposed in numerous patents. In Size et al. US. Pat. No. 3,602,381 a tailgate lift of the general type with which the present invention is concerned is disclosed. In this patent, however, the same power-operated means that moves the platform from ground level to bed level also serves to mo ve the platform from bed level to gate-closing position. With the structure of the Size patent, a latch is relied upon to maintain the platform in gate-closing position. This fails to prevent vibration during transit and also creates a dangerous situation in that, if the latch is released inadvertently, the tailgate will fall by gravity and may cause accidents. In addition, with the construction of the Size patent, there is a complicated interlock, embodying fine adjustments. which is intended to prevent inadvertent actuation of the mechanism to move the platform to or from tailgate-closing position. However, if such interlock is not properly adjusted, it is entirely possible that the gate may fall prematurely by gravity and cause an accident.

There are other types of constructions wherein there are cam arrangements for controlling the movement to and from gate-closing position. These cams are complicated and, if they are not installed properly, there are problems and danger. In addition, with constructions utilizing cams, the size of the gate platform is limited.

SUMMARY OF THE INVENTION The present invention provides a novel tailgate lift mechanism embodying parallelogram-type linkage wherein there is power-operated means for moving the platform from ground level to bed level, and wherein there is separate and independent power-operated means coupled with a novel linkage arrangement for moving the platform from bed level to tailgate-closing position, the linkage being worked out in a novel way so that it moves to an over-center position when the gate is closed to cause a mechanical bind and positively prevent the platform from accidentally moving from the closed (transit) position to the open (use) position. The arrangement provides for full controlled power closing of the gate and opening only by using power to retract the linkage out of the over-center position.

A general object of the invention is to provide an improved tailgate lift wherein there is one poweroperated means for controlling the movement between ground level and bed level, and wherein there is a second power-operated means for controlling movement from bed level to tailgate-closing position, the latter embodying linkage which moves to an over-center position when the gate is closed.

A further object of the invention is to provide a tailgate lift as above described in which opening of the gate can only be accomplished by use of the gatecontrolling power means.

A further object of the invention is to provide tailgate lift mechanism which eliminates the necessity of utilizing cams or interlocks to control the movement to and from tailgate-closing position.

A more specific object of the invention is to provide a tailgate lift as above described wherein the power means for moving from bed level to tailgate-closing position includes a double-acting hydraulic cylinder, together with a linkage arrangement which moves to an over-center position when the gate is in closing posi-' tion, it being necessary to operate the hydraulic cylinder in order to move the gate to open position.

Other objects of the invention are to provide a tailgate lift which is relatively simple and foolproof in operation, which holds the gate firmly in closing position eliminating excessive movement, and insures againstv accidental dropping of the gate, and which can be employed with any size gate which is normally encountered.

With the above and other objects in view, the invention consists of the improved tailgate lift mechanism and all of its parts and combinations, as set forth in the claims, and all equivalents thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of the tailgate lift mechanism showing it associated with the rear end of a truck body bed, parts being broken away and shown in section, the full lines showing the parts in bed level position and the phantom lines showing the platform and its linkage in ground level position;

FIG. 2 is a similar view showing the parts in gateclosing position;

FIG. 3 is a fragmentary perspective view looking principally from the rear of the vehicle while the parts are in the position which they assume when the platform is at ground level;

FIG. 4 is a fragmentary perspective view looking more directly from the rear;

FIG. 5 is a perspective view looking principally at the opposite side of the mechanism from that shown in FIG. 3 to show the gate-closing cylinder and its associated mechanism; and

FIG. 6 is a diagram to illustrate the positions of the linkage, showing the over-center sequence as the platform goes into full closed position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring more particularly to the drawings, the numeral 20 designates a platform which serves to lift loads from ground level to the level of the vehicle bed 19 as illustrated in FIG. 1, and which can also be swung upwardly to serve as a tailgate as in FIG. 2. The forward ends of the sides of the platform have depending ears 21 which form parts of the parallelogram linkage and to which the ends of parallel arms 22 are connected as at 23. The other ends of the parallel arms are pivotally connected as at 24 to pivot links 25 which form a part of the parallelogram linkage and which are also pivoted as at 26 to brackets 27, the latter being welded rigidly to a supporting member 28. The member 28 is supported by the lower ends of side mounting plates 18, the latter being suitably mounted on the vehicle and/or bed. Also pivoted to the front end of the platform, one on each side, as at 29, is a pair of lift arms 30. The other ends of the lift arms 30 are pivoted to the brackets 27 on pivots which are in axial alignment with the pivots 26 for the pivot links 25. The parallel arms and lift arms 22 and 30 form portions of the parallel linkage mechanism. A cross-member 31 rigidly connects forward portions of the lift arms. Projecting from the cross-member in one direction are spaced ears 32 which carry a latching pin 33 which is adapted to be engaged by a pivoted latch 34 pivoted at its inner end as at 35, on spaced frame parts 36.

Pivoted as at 37 between support 38 projecting from the frame members36 is one end ofa double-acting hydraulically actuated closing cylinder 39. The latter has an extensible piston rod 40 with an adjustable end 46 which is pivotally connected as at 41 between one extension 42 of a bell crank. The latter is rigid with a cross-shaft 43. The other extension 44 of the bell crank is connected by an adjustable tie rod 45 with pivot link 25. This pivot is designated 47 and the pivot connection with the bell crank lever is designated 48.

The movement of the platform from ground level to bed level is under the control of a single acting or double-acting hydraulic cylinder 49 which is pivoted at its upper end to the frame member 36, as at 50, and has an extensible rod 51 pivotally connected as at 52 between ears 53 which project from the cross-member 31 as shown in FIGS. 2 and 3.

Operation In operation, assuming that the platform is in the broken line ground level position of FIG. 1, by retracting the rod 51 of the cylinder 49, a load can be lifted to a convenient position for loading onto the floor 19 of the truck body. As the platform approaches the floor or bed level position shown in full lines in FIG. 1, the pin 33 will snap into engagement with the latch 34 in the manner illustrated. To lower the platform, the latch 34 must be released through any convenient control mechanism. Next, where the cylinder 49 is singleacting, the retracting pressure on the cylinder 49 is relieved, and the platform is permitted to lower by gravity from the full line position of FIG. 1 to the broken line position therein. If the cylinder 49 is double-acting, the platform may be powered down.

After the truck has been loaded and it is desi'red to close the tailgate, the platform being at bed level, then the piston rod 40 of the cylinder 39 is retracted. This causes clockwise rotation of the bell crank levers 42-44 from the position of FIG. 1 to the position of FIG. 2. During such movement the tie rods 45 push on the pivots 47 of the pivot links to push the parallel arms 22 from the position shown in FIG. 1 to the position shown in FIG. 2. During such movement, the upper ends of the arms exert pressure on the pivot points 23 to rotate the platform from the horizontal position of FIG. 1 to the vertical position of FIG. 2 about point 29, where it acts as a gate, closing the rear end of the truck body.

As a principal feature of the present invention, when the gate 20 arrives at the vertical position of FIG. 2, the knee pivots 48 move just below the center line C of FIG. 6, which center line extends through the pivots 43 and 47 to lock the parts in an over-center closing position. This provides a firm closure and holds the platform 20 against excessive movement when it is in gateclosed position. In addition, and of major importance, is the fact that the over-center movement of the knee pivots 48 with respect to the center line C through the pivots 43 and 47 positively prevents accidental dropping of the platform. Thus accidents are prevented. A suitable stop 60 is employed in combination with adjustable piston rod end 46 and adjustable tie rods 45 to prevent the linkage from going too far over center. In commercial practice, the linkage should go approximately 2 past center, which provides a rigid lock.

The over-center locking feature is illustrated diagrammatically in FIG. 6 in somewhat exaggerated style. Here, position 1 shows the relative position of the critical parts before reaching center as the gate is being closed. Position 2 shows the three pivot points directly on center, and position 3 shows the over-center position of pivot 48 with respect to the center line C.

The platform can only be moved from the position of FIG. 2 by powering it down through operation of the hydraulic closing cylinder 39. This is accomplished by causing extension of the piston rod 40 which acts on the bell crank levers 42-44 to swing the bell cranks in a counterclockwise direction. At the start of this movement the pivot points 48 are unlocked from their overcenter position, and continued movement causes controlled opening of the gate under control of the hydraulic cylinder 39, with return of the platform to bed level position. To lower the platform to ground level, the latch 34 is released from the pin 33 through any suitable control, and the platform is permitted to lower to ground level under the influence of gravity when the cylinder 49 is single-acting. If cylinder 49 is doubleacting, the platform may be powered down.

From the above it is apparent that, with the improved construction, the necessity of using cams and complicated interlocks is eliminated. It is also apparent that the over-center locking of the platform in tailgateclosing position prevents vibration of the gate during transit, and also positively prevents the gate from falling prematurely and causing accidents. With the construction of the present invention, there is full power closing from bed level to gate-closing position.

In addition, the construction of the present invention provides for a slow gate-closing rate. This is advantageous from the safety standpoint. Inasmuch as the opening of the gate must be performed hydraulically, the linkage of FIG. 5 will not retract from the overcenter position until the control valve for the hydraulic cylinder 39 is manipulated. Due to the fact that there are no cams required with the present construction, the features of the present invention may be readily used with large-sized platforms.

Various changes and modifications may be made without departing from the spirit of the invention, and all of such changes are contemplated as may come within the scope of the claims.

What we claim is:

1. In a tailgate lift for vehicles of the type having a bed with a tailgate opening for receiving loads, in which said lift has a fixed frame, has a platform, has linkage for movably connecting said platform to said frame and has power-operated means for moving said platform from ground level to bed level, the improving comprising: separate power-operated means on said frame for controlling movement of the platform from bed level to an upright tailgate-closing position, an element pivoted to said fixed frame, a fluid pressure operated ram having one end pivotally connected to the fixed frame and having its other end pivotally connected to said pivoted element to swing the latter, and a connecting element pivoted at one end to said pivotal element and at its other end to said linkage, said connecting element having an intermediate knee pivot which is movable over center with respect to the pivotal connection for said pivoted element and with respect to the pivotal connection with said linkage.

2. In a tailgate lift for vehicles of the type having a bed with a tailgate opening for receiving loads, in which said lift has a frame, has a platform, has linkage for movably connecting said platform to said frame and has power-operated means for moving said platform from ground level to bed level, the improvement comprising: separate power-operated means on said frame for controlling movement of the platform from bed level to an upright tailgate-closing position, said separate power-operated means including a knee pivot movable to an over-center position when the platform is in upright position to mechanically lock the platform in said tailgate-closing position, said tailgatecontrolling linkage including a first element pivoted to the frame and having an extension, and a connecting element pivoted at one end to said extension to provide a knee action and at its other end to said linkage, and the knee action pivot being movable over center with respect to the pivotal connection for said element having the extension and with respect to the pivotal connection with said linkage.

3. A tailgate lift as claimed in claim 2 in which the first pivoted element having an extension is a bell crank lever.

4. A tailgate lift as claimed in claim 2 in which the power-operated means includes a fluid pressure operated ram connected to the frame, and in which the first pivoted element is a bell crank lever having one extension to which the ram is pivotally connected and having another extension which is pivotally connected to the connecting element.

5. In a tailgate lift for vehicles of the type having a bed with a tailgate opening for receiving loads, in which said lift has a frame, has a platform, has linkage for movably connnecting said platform to said frame and has power-operated means for moving said platform from ground level to bed level, the improvement comprising: separate power-operated means on said frame for controlling movement of the platform from bed level to an upright tailgate-closing position, said separate power-operated means including a knee pivot movable to an over-center position when the platform is in upright position to mechanically lock the platform in said tailgate-closing position, the separate poweroperated means comprising a fluid pressure operated ram, a bell crank lever pivoted to the lift frame and having one extension pivotally connected to the ram and having a second extension, a connecting rod pivotally connected at one end to said second extension and at its other end to said linkage, the pivot which is connected to the second extension being movable to an over-center position with respect to the pivot for the bell crank and with respect to the pivotal connection with the linkage when the platform is in upright position to mechanically lock the platform in said tailgateclosing position.

6. A tailgate lift as claimed in claim 5 in which the bell crank lever includes a shaft pivotally connected to the frame, and in which said bell crank extensions are rigid with said shaft but spaced from each other axially of the shaft.

7. In a tailgate lift for vehicles of the type having a bed with a tailgate opening for receiving loads, in which said lift has a frame, has a platform, has linkage for movably connecting said platform to said frame and has power-operated means for moving said platform from ground level to bed level, the improvement comprising: separate power-operated means on said frame for controlling movement of the platform from bed level to an upright tailgate-closing position, said separate power-operated means comprising: a crank arm pivoted to the lift frame, means for causing pivotal movement of said crank arm, a connecting rod pivotally connected at one end to said crank arm and at its other end to said linkage, the pivot which is connected to said crank arm being movable to an over-center position with respect to the pivot for the crank arm and with respect to the pivotal connection with the linkage when the platform is in an upright position to mechanically lock the platform in said tailgate-closing position. l 

1. In a tailgate lift for vehicles of the type having a bed with a tailgate opening for receiving loads, in which said lift has a fixed frame, has a platform, has linkage for movably connecting said platform to said frame and has power-operated means for moving said platform from ground level to bed level, the improving comprising: separate power-operated means on said frame for controlling movement of the platform from bed level to an upright tailgate-closing position, an element pivoted to said fixed frame, a fluid pressure operated ram having one end pivotally connected to the fixed frame and having its other end pivotally connected to said pivoted element to swing the latter, and a connecting element pivoted at one end to said pivotal element and at its other end to said linkage, said connecting element having an intermediate knee pivot which is movable over center with respect to the pivotal connection for said pivoted element and with respect to the pivotal connection with said linkage.
 2. In a tailgate lift for vehicles of the type having a bed with a tailgate opening for receiving loads, in which said lift has a frame, has a platform, has linkage for movably connecting said platform to said frame and has power-operated means for moving said platform from ground level to bed level, the improvement comprising: separate power-operated means on said frame for controlling movement of the platform from bed level to an upright tailgate-closing position, said separate power-operated means including a knee pivot movable to an over-center position when the platform is in upright position to mechanically lock the platform in said tailgate-closing position, said tailgate-controlling linkage including a first element pivoted to the frame and having an extension, and a connecting element pivoted at one end to said extension to provide a knee action and at its other end to said linkage, and the knee action pivot being movable over center with respect to the pivotal connection for said element having the extension and with respect to the pivotal connection with said liNkage.
 3. A tailgate lift as claimed in claim 2 in which the first pivoted element having an extension is a bell crank lever.
 4. A tailgate lift as claimed in claim 2 in which the power-operated means includes a fluid pressure operated ram connected to the frame, and in which the first pivoted element is a bell crank lever having one extension to which the ram is pivotally connected and having another extension which is pivotally connected to the connecting element.
 5. In a tailgate lift for vehicles of the type having a bed with a tailgate opening for receiving loads, in which said lift has a frame, has a platform, has linkage for movably connnecting said platform to said frame and has power-operated means for moving said platform from ground level to bed level, the improvement comprising: separate power-operated means on said frame for controlling movement of the platform from bed level to an upright tailgate-closing position, said separate power-operated means including a knee pivot movable to an over-center position when the platform is in upright position to mechanically lock the platform in said tailgate-closing position, the separate power-operated means comprising a fluid pressure operated ram, a bell crank lever pivoted to the lift frame and having one extension pivotally connected to the ram and having a second extension, a connecting rod pivotally connected at one end to said second extension and at its other end to said linkage, the pivot which is connected to the second extension being movable to an over-center position with respect to the pivot for the bell crank and with respect to the pivotal connection with the linkage when the platform is in upright position to mechanically lock the platform in said tailgate-closing position.
 6. A tailgate lift as claimed in claim 5 in which the bell crank lever includes a shaft pivotally connected to the frame, and in which said bell crank extensions are rigid with said shaft but spaced from each other axially of the shaft.
 7. In a tailgate lift for vehicles of the type having a bed with a tailgate opening for receiving loads, in which said lift has a frame, has a platform, has linkage for movably connecting said platform to said frame and has power-operated means for moving said platform from ground level to bed level, the improvement comprising: separate power-operated means on said frame for controlling movement of the platform from bed level to an upright tailgate-closing position, said separate power-operated means comprising: a crank arm pivoted to the lift frame, means for causing pivotal movement of said crank arm, a connecting rod pivotally connected at one end to said crank arm and at its other end to said linkage, the pivot which is connected to said crank arm being movable to an over-center position with respect to the pivot for the crank arm and with respect to the pivotal connection with the linkage when the platform is in an upright position to mechanically lock the platform in said tailgate-closing position. 